Copper-extraction process



Jan, 3, 1928. 1,654,930

W. E. GREENAWALT COPPER EXTRACTION PROCESS Filed Aug. 13. 1926 Mme Ora Sulphide Ore Oxldlzed Ore. or Concentrate Leachmg Tank Roastmg Fu mace SO RecLucer Impoverishecl Coppe r Soluclon -cld +Ec,(5O4)3) E lectrolyzed. Spluhon (Acl ci+Fc L5o b Co er Ta l ks acid UNITED S'TATESIPATENT OFFICE.

WILLIAM E. GREENAWALT, 01 DENVER, COLQBADQ.

COPPER-EXTRACTION PROCESS.

Application filed August 18, 1926. Serial No. 129,038.

The process relates generally to the production of electrolytic copper from its ores by leaching and electrolysis, and more specifically to the preparation of the solution before electrolysisi The process may beconsidered as an improvement in details on the more general process described in my Patents No. 1,353,995, September 28, 1920, and No. 1,483,056, February 5, 1924'.

In the electrolysis of impure copper solutions as for example those obtained from leaching copper ore with an acid sulphate solution, there is always present iron sulphate, which injuriously affects the operation. Ferrous sulphate in the electrolyte is not particularly harmful and may be beneficial, but the ferric sulphate is highly detrimental. v

If a solution of copper sulphate, containing ferrous sulphate, is'electrolyzed, copper is deposited at the cathode while sulphuric and ferric sulphate are produced at the anode, as shown by the following equation:

in which a: represents an indeterminate amount of sulphuric acid and y an indeterminate amount of ferric sulphate. The relative amounts of acid and ferric sulphate produced by the electrolysis will largely depend on. the details of operation, such as the iron content of the electrol te, the temperature of the electrolyte, and't e composition of the' anodes.

The ferric sulphate, finding its way to the cathode, combines with the deposited copper, and is again reducedto the ferrous condition, thus:

The loss of efliciencyin the deposition of the copper is more or less proportional to the amount of ferric sulphate in the electrolyte,

and under certain conditions may be very large. In aggravated cases the loss-of efficiency may dissolved as rapidly as it is deposite however, the ferric sulphate can be reduced to the ferrous condition at the expense of a e so great that the cop er is If,

cheap reducing agent, the process can be operated smoothly and effectively.

sulphur dioxide on ferric sulphate maybe expressed by the equation: F e (S0,) S0 +2H O=2FeSO,+2H SO,. 00

The reaction is not very rapid, and in carrying it out the solution, after most of the ferric iron has been reduced, may contain an excess of sulphur. dioxide. This, at times, may be desirable and beneficial. At other 5 times, as in cases of poorly v ntilated electrolytic cell rooms, the excess su phur dioxide may be objectionable. The small excess of sulphur dioxide can fairly well be controlled by providin a storage tank for the solution, after the su phur dioxide application, and, as the reaction between the small amount of unreduced ferric iron and the small amount of unconsumed sulphur dioxide is fairly slow, conditions can be arranged so that much or all of the excess sulphur dioxide can be consumed in the storage tank in acting on the small amount of remaining ferric iron, or in being oxidized to sulphuric acid.

It may be desirable at times to neutralize 8o ordestroy the excess sulphur dioxide more quickly t nm by the method described, and this can .be done conveniently by applying a. gas, such as hydrogen sulphide, to the solution containing only a small amount of sulphur dioxide. The reaction, in solution, between small quantities of sulphur dioxide and hydrogen sulphide is quite rapid, and

may be represented by the equation; 3 1OH SO IOH S=2H S O +5S'+18H,O,

It is preferred to apply the H 8 in very dilute form, corresponding somewhat to the dilution of the sulphur dioxide in the copper solution. This will tend to give the greatest elimination of sulphur dioxide vwith the least precipitation of copper sulphide.

If there is an excess of. hydrogen sulphide,

the hydrogen sulphide also acts as a reduc- 7 mg agent for remaining small amounts of ferric iron, as shown by the equation:

Fe (SO tH S=2FeSO,+H SO +S.

Excess hydrogen sulphide would also immediately act on the copper in the solution, according to the equation,

I If the hydrogen sulphide precipitates copper from the solution as copper sulphide, the

copper sulphide precipitate will also act as a reducing agent for the ferric iron, thus:

Fe, (S0 3 Gus ()uSO +2FeSO;,+ S.

The process may conveniently be illustrated by thevaccompanying drawing, which is a flow sheet in diagrammatic plan. The ore, which may be assumed as a sulphide ore or concentrate, is roasted in the roasting furnace under conditions suitable for leaching.

The roasted ore is treated in the leaching tank with a dilute acid solution to extract the copper. The resulting copper solution,

. sulphur dioxide in the reducer flows into the settler, which also acts asa storage tank, where the solution is clarified, and further time is given for the excess sulphur d'ioxide to. react with excess ferric iron. In this way practically all of the sulphur dioxide will be consumed, and. conditions can be arranged so that there will be little or practically no sulphur dioxide left in the solution as it leaves the settling and storage tank. In order, however, to avoid contamination of the atmosphere in the cell room by a possible excess of sulphur dioxide, which ma escape from the solution during electro ysis, the solution issuing from the settler is treated with verydilute hydrogen sulphide, which -quickly destroys the small amount of excess sulphur dioxide, as described. The hydrogen sulphide cannot have any harmful effect on the atmosphere of the cell room. The hydrogen sulphide will be immediately consumed in reacting with the sulphur dioxide, ferric sulphate, and the copper in the solution before there can be any excess, and as the amount of hydrogen sulphide applied to the copper solution is very small, theoretically only enough to combine with the very small amount of excess of sulphurdioxide, there will be no contamination of the atmosphere of the cell room with either sulphur dioxide or hydroggn sulphide, for the reason that both will destroyed. If desired the hydrogen sul-.

phide may be added to the solution before it flows into the settler and storage tank, but it is preferred to add it after it issues from the settler. The reduced copper solution,

. freed from excess sulphur dioxide, then flows into the electrolytic copper tanks, where copper is deposited and acid and ferric iron are regenerated. A portion of the solution is preferably circulated between the S0 reducer, the settler and the electrolyzers to impoverish the solution in copper to the desired amount while another portion-the advance flowis returned to the leaching tank to pass through another complete cycle.

While hydrogen sulphide is preferred to destroy the excess $0 after the ferric iron is reduced to the ferrous condition, other agents, such as chlorine, may be used. Hydrogen sulphide is easily obtained and easily applied in small quantities, and chlorine may be undesirable in a sulphate electrolyte. In a chloride electrolyte chlorine would not be objectionable as a destroyer of excess sulphur dioxide. In any case there would not be free chlorine in the electrolyte, nor would there be any free sulphur dioxide.

To further control the amount of sulphur dioxide in the solution before electrolysis, it may be desirable at times to return a portion. of the solution from the electrolyzers direct to the'storage tank, where the ferric iron in the solution from the electrolyzers may react with the small excess of sulphur dioxide in the reduced solution in the storage tank. A balance can easily be mam-V brought into intimate contact with the very dilute sulphur dioxide in the solution, so that the excess sulphur dioxide will be destroyed with the least consumption of hydrogen sulphide or other reacting gas.

Sometimes it is desirable to have very small amounts of chlorine in sulphate solutions, especially if the solution contains small amounts of silver, as silver sulphate, for example. In such cases chlorine could be used to advantage in destroying excess sulphur dioxide.

I claim:

1. In the deposition of copper from solutions obtained from leaching copper ore and containing salts of iron the process comprising, electrolyzing the solution, treating the electrolyzed solution with sulphur dioxide, then treating the solution with hydrogen sulphide, and then again electrolyzing the solution.

2. In the deposition of metals from solutions obtained from leaching ore and containing salts of the variable valent elements the process comprising, electrolyzing the solution, treating the el'ectrolyzed solution with a gaseous reducing agent, destroying excess of the gaseous reducing agent with another gaseous reagent, and again electrolyzing the solution. r

3. A copper extraction process comprising, leaching copper ore with an acid solution to extract the copper, electrolyzing the resulting copper solution containing salts of .iron to deposit the copper and regenerate acid and ferric iron, applying sulphur dioxide to the solution as a reducing agent for the ferric iron produced by the deposition of the copper, then applying hydrogen sulphide to the solution to destroy the excess of sulphur dioxide, again electrolyzing the solution and the solution to the ore to pass through another complete cycle. I

4. A copper extraction process comprising, leaching copper ore with an acid solution to extract the copper, electrolyzing the resulting copper solution containing salts of iron to deposit the copper and regenerate acid and ferric iron, treating the electrolyzed solution with sulphur dioxide to reduce ferric iron to the ferrous condition, maintaining a pool of the solution after sulphur dioxide reduction, applying a reagent to the solution to destroy excess sulphur dioxide, again electrolyzing the solution, circulating a portion of the solution between the electrolyzer and the reducer, and returning a portion of the solution from the electrolyzer to the ore to pass through another complete cycle.

5. In the deposition of copper from solutions obtained from leaching ore and containing salts of iron the process comprising, electrolyzing the solution, treating the electrolyzed solution with sulphur'dioxide, then treating the solution with hydrogen sulphide diluted with air, and again electrolyzing the solution.

WILLIAM E. GREENAWALT. 

